# “Percent” vs. “percentile”

Just because .01% of people may be at risk of frying themselves on the third rail doesn't mean they need to modify the system for that miniscule percentile. It just means you need to let Darwinism run its course.

What's the difference between percent and percentile? And how do I use percentile in context?

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The usage in the quote you gave is wrong. It should be 'percent'. Any dictionary will tell you why. – Mitch Jul 12 '12 at 17:01
Actually, it should be percentage. – TimLymington Jul 12 '12 at 20:41

Percentile is not equivalent to percent, and I don't think the quoted text is using it in quite the right way (it's abusing the term Darwinism as well, but I guess that's for a separate question).

A percentage is simply a representation of a proportion out of 100. To say three out of every six is the same as to say fifty out of every hundred, in other words fifty percent (from the Latin per centum).

A percentile is a statistical measure of distribution. For a given set of data, it is the level below which a certain percentage of the data falls. In graphic terms, it represents the area under the curve of a distribution.

For a more human example, if you score in the 72nd percentile on an exam, it means you scored higher than 72 percent of all the people who took the same exam— regardless of what your actual score was. If your baby is in the 28th percentile for length, it means she is longer than 28 percent of all comparable babies (e.g. babies at a certain age).

Related terms include decile, quintile, quartile, tertile, if you divide up your population by 10, 5, 4, or 3 instead of 100.

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This is all true. If I scored in the 75th percentile on an exam, that tells me that I scored higher than 75% of the test-takers – but I may have fared even better as well, depending on the granularity of the reporting. In other words, some reports will tell you where you placed to the nearest percentile; others will simply indicate, say, which quintile you placed in. In the latter case, if your score was reported as "in the 2nd quintile," then you scored at least at the 60th percentile, but possibly as high as the 79th. – J.R. Jul 12 '12 at 17:15
So J.R. numbers his percentiles starting from the bottom, but his quintiles starting from the top. – GEdgar Jul 12 '12 at 21:29
@GEdgar: Nice "gotcha." Sometimes, though, when dealing with scores and academic rankings, the order does get inverted, just as you point out – presumably because it's more intuitive to have the "best" students in the "top" division. It's not just me who does this; a Univ. of Arizona publication reads: "Applicants from a regionally accredited high school may demonstrate aptitude for academic work by ranking in the 75 to 100 percentile (upper 25 percent/first quartile) of their high school graduating classes." – J.R. Jul 12 '12 at 22:15

I have encountered "percentile" on Sporcle. For example, if you come 200th out of 1000 quiz-takers, you are said to be in the 80th percentile (I think). Percentile is a noun, whereas percent is a Latin phrase meaning "per hundred". An example of where you would use percent but not percentile might be "50 per cent of adult males have brown hair".

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@Charles Are you sure? – JamesHH Jul 12 '12 at 19:08
actually, no. you're right. i understood "200th" wrongly somehow.... – Charles Jul 12 '12 at 20:04

In other words the difference between percent and percentile is clear from this that in a particular examination you can calculate the number of candidates falls within top determined percentile on the basis of total number of students appeared in the examination but you can't calculate total number of students falls within that predetermined percentage (I think). For example in an examination if number of students appeared is 100 then we can calculate that approximately 20 students will fall within top 20 percentiles whereas we are unable to calculate that how many students will fall within top 20 percent in that exam.

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Welcome to EL&U. I'm not sure you're correct on this. Please provide links to sources which support your answer. :) – medica Jan 6 '14 at 4:28

To me it seems vise versa. You could say that 20 people would be in the top20%, but you could not say how many would be in top 20 percentile since the percentile the distribution would be known only after the exam and than you would know how many people would be in top 20 percentile.

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Not true. You do know how many people will be in the top 20 percentile if you know the sample size. You just don't know who they will be. – Chenmunka May 22 '14 at 18:27

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